This invention relates to a method of characterizing the occupant of a motor vehicle seat for purposes of allowing or suppressing air bag deployment based on sensed occupant weight, and more particularly to a method of distinguishing an empty seat from a seat having an ultralight child seat placed on it.
Vehicle occupant weight detection systems are useful in connection with air bags and other pyrotechnically deployed restraints as a means of characterizing the occupant for purposes of determining whether to allow or suppress deployment of the restraints. For example, it is generally desired to allow deployment for a child or small adult, and to suppress deployment (or reduce deployment force) for a small child. In the case of infant or child seats (referred to herein collectively as child seats) that are placed on the vehicle seat and cinched down with a seat belt, it is generally believed that deployment should be suppressed entirely.
As disclosed in U.S. Pat. No. 6,246,936, issued Jun. 12, 2001 and assigned to the assignee of the present invention, a tightly cinched child seat can be distinguished from a small adult (such as a 5th percentile adult female) by detecting the variation in the sensed weight during vehicle movement. The occupant is characterized as a child or small adult if the variation exceeds a threshold, whereas the occupant is characterized as a child seat if the variation is below the threshold, as a tightly cinched seat belt severely restricts variance.
An issue that is not addressed in the above-mentioned patent application, however, concerns distinguishing between an empty seat and a seat occupied by an ultralight child seat of the type designed for newborn babies. Although deployment of the inflatable restraints will be suppressed in either event (empty seat or small child), it is important to know when the seat is truly empty for purposes of adaptive calibration. Additionally, in applications where the occupant characterization and suppression status are displayed for driver verification of proper system operation, it is confusing for the displayed status indicate empty seat when an ultralight child seat is present. Accordingly, what is needed is a method of more accurately distinguishing between an empty seat and a seat occupied by an ultralight child seat, and for displaying an accurate status message to the drive of the vehicle.
The present invention is directed to an improved weight-based occupant characterization method that reliably distinguishes between an empty seat and a seat occupied by an ultralight child seat. According to the invention, the seat occupancy is initially characterized using a primary classification methodology in which the measured seat pressure is compared to an allow threshold representative of a minimum weight adult. If the primary classification methodology determines that the seat is empty and a seat belt for the passenger seat is buckled, a secondary classification methodology is initiated to compare the measured seat pressure to a predetermined pressure range characteristic of occupied ultralight child seats. If the measured pressure falls within the ultralight child seat range, characterization of the primary classification methodology is discarded in favor of the characterization of the secondary classification methodology.